Overview

The San Francisco Bay Area is home to many radio amateurs and has an active APRS network. The San Francisco Bay Area terrain offers some of the best digipeater siting in the world. From almost anywhere in the central Bay Area you will have line-of-sight and clear reception to at least one high-level mountain-top digipeater. Exceptions to this are of course in areas such as the "urban canyon" of San Francisco, parts of the western side of the Coastal Range mountains from Santa Cruz north to Pescadero, the eastern side of the Diablo Range from Mt Hamilton north to Pleasanton, etc.

Challenges

Due to the large number of APRS users, the 144.390 APRS frequency is almost constantly in use and efforts are always being made to reduce excessive or redundant packets. Use of "old paradigm" digipaths (RELAY and WIDE and TRACE and TRACEn-N) is strongly discouraged and most if not all San Francisco Bay Area digipeaters will no longer respond to these paths.

Solution: Digipeater Siting Strategy

The near-ideal geographic layout of the region implies there is usually no reason for an APRS user to set up and run low-level, supplemental, or fill-in digipeaters within the central Bay Area. Doing so will almost always generate redundant packets which increases collisions and channel traffic, reducing throughput. Exceptions to this may be in urban canyons, pocket valleys, or remote areas along the coast where it can be demonstrated that a mobile station's packets do not otherwise reach the network. A special event occurring in such remote "shaded areas" may benefit from a temporary "fill-in or event" digi (which only responds to packets addressed via WIDE1-1 or it's own callsign) sited overlooking the operating area for the event duration.

If you have reason to believe that a supplemental or fill-in digipeater is needed routinely, you could join the California APRS Users Group (hosted on Yahoo Groups) and post a proposal detailing where and why. The folks there will help you determine proper settings to ensure that your digipeater is beneficial to the local users.

Solution: Receive-Only IGate Strategy

FM capture effect at Bay Area digipeaters is an issue; distance and channel congestion often results in a higher-powered station (mobile or base) covering packets from a lower-power mobile or handheld. Therefore those wishing to contribute to the local APRS system are encouraged to consider establishing receive-onlyIGates instead of supplemental or fill-in digipeaters. These receive-only IGates pass packets heard on RF to the Internet via APRS-IS but do not add duplicate packets to the VHF airwaves as another digi could.

Solution: Localizing Paths

Even with the "new paradigm" paths (WIDEn-N) being implemented there are still occasionally cases where local traffic will wander in or out of the Northern California region. To reduce this, high-level network "S overlay" digipeaters (and some stations) have started using the NCAn-N in place of WIDEn-N paths. This ensures that packets intended for Northern California users remain within the region. Digis and other fixed stations are encouraged to beacon local information locally, with no path, and beacon position with a path once an hour. Most digies trap abusive paths, many trap WIDE3-3, and some high level Digies even trap WIDE2-2. Fill-in digis usually only respond to WIDE1-1, and do not respond to packets addressed via NCA1-1. So a mobile station could use a path of WIDE1-1,NCA1-1 instead of the routine WIDE1-1,WIDE2-1 mobile path. Commuters in areas that have I-gates and digis nearby could simply use WIDE1-1. Taming paths and timing to our intended audience shows good amateur practice, and can help alleviate network overload. We have helpful web sites like APRS.FI RAW that make it easy to examine our own settings. Northern California's APRS HOGS web site can help those of us within it's ear shot to attempt to stay off the top of the "Hogs" list. Check to see if your call shows up on the APRS Errors list (It's a big list, put the callsign in your browser's find/search tab to parse). These tools can help us find the settings that work best for our own needs. Ultimately each individual chooses the settings that they require for their own enjoyment of the hobby. Hopefully not at the expense of others.

Recommended path settings for mobile stations

WIDE1-1,WIDE2-1 : Two hops in all directions with potential to use fill-in digis. Best routine, and for events.

WIDE1-1,WIDE2-2 : Three hops in all directions. Not normally required; use is discouraged. (Potential to be propagated out a thousand miles, by up to 36 distant digipeaters).

WIDE1-1 : "Commuters" may find that a short mobile path of WIDE1-1 is adequate for their needs.

NCA1-1 : or NCA2-2 can be used if you don't travel outside the Northern California (NCA) region. No access to fill-ins

Aircraft are recommended to use a single hop path, or no path when at high altitude. (WIDE1-1, or WIDE2-1, or NCA1-1 in NORCAL)

Recommended path settings for fixed, non-moving stations

WIDE2-1 : One hop... Suitable if you are within earshot of a "high" WIDEn-N digi with a large footprint. Avoids use of all fill-in digis.

WIDE2-2 : Two hops in all directions... recommended maximum for routine use in most areas.

WIDE3-3 : Three hops in all directions. Not normally required, use is discouraged, many digis trap WIDE3-3 and higher

NCA1-1 : or NCA2-2 may be used. NCA1-1 is more courteous, and is equivalent to WIDE2-1.

WIDE1-1 : Use is discouraged for fixed stations unless your target is a fillin digi.

RELAY and WIDE and TRACE and TRACEn-N are obsolete and strongly discouraged.

Recommended timing settings for mobile

Position Beacon : While moving, a beacon rate of once a minute, with a single hop path (WIDE1-1) would be about the fastest TX rate a local network could handle. Many courteous users set 3 to 10 minute beacons, with a routine two hop path (WIDE1-1,WIDE2-1). Smart Beaconing is recommended over timed beaconing when available. Powering Trackers from the Ignition switch or using a Power off timer is recommended. Leaving a mobile tracker on while stationary, with a TX rate of more than once or twice an hour can cause a great load on our RF network over time. Look at the top few users at APRS Hogs, several users let their TNC's transmit at a rapid rate, 24/7. It wouldn't take many uninformed users to overload our precious frequency, that we all have to share. Ultimately it's up to each individual to decide what settings are required for their intended audience.

Smart Beacon : SmartBeaconing™ transmits beacons depending on speed and direction. This technique is more channel efficient than simple time based beaconing, as it dynamically reduces the number of packets being sent as the unit velocity decreases. The default settings are courteous. Changing the default settings could be detrimental to the network. If the Bay Area APRS.FI map shows someone's tracks as a constant red line, they might have changed smart beacon settings, or Position timing to a rate that adversely affects the RF network.

Stationary Mobile : Non moving objects should TX similar to fixed stations, once or twice an hour is courteous, and will keep an object on the maps. A stationary mobile that's beacon rate is at once every 10 minutes could be considered a spammer, that's 144 worthless beacons in 24Hrs. Properly setup SmartBeaconing™ transmits a packet once every 30 minutes while stationary, which compensates for the sometimes "spastic" beaconing while CornerPegging™. Setting APRS DC power to vehicle's ignition switch, or use of a timed power off relay is advised to limit needless QRM.

Status Message : Many Trackers can be set to send a status message once every 10 or 15 position beacons, instead of with every position beacon. This allows quicker air time, less chance of packet collisions, and an increase in successful packets to APRS-IS. Trimming long messages, telemetry, Altitude, TX delays... Can also increase successful packets.

TX Delay : In the old days 300 milliseconds was the standard. Today in the age of PIN diodes 180 milliseconds should be more than enough.

MIC-E : Compression can cut air time by more than 50%. Short packet bursts have a much greater success rate, especially in busy Northern California.

Recommended timing settings for fixed, non-moving stations

Position Beacon : Position beacons with a path of WIDEn-N, or NCAn-N, are recommended once an hour, any additional position beacons with no path.

Status-Local info : Repeaters, EchoLink, and IRLP objects are recommended not more often than once every 10 minutes without a path. Keep your local info local.

TX Delay : 180 Milliseconds is recommended.

Recommended settings for Digipeaters

Carrier Detect Software detect is superior to using squelch, it's fast, (squelch off, set to noise all the time) no squelch delays on decode, or TX delays from noise.

Preempt is recommended on WIDEn-N Digis that have aliases like: SSn-N or SAR.

Position Beacon : Position beacons with a path of WIDEn-N, or NCAn-N, are recommended once an hour, any additional position beacons with no path. WIDE2-1 or NCA1-1 is adequate for high level Digis. (The latest recommended digi settings from Bob, WB4APR are: Fillin || KPC-3 ver 8.2 || KPC-3+ || UIDIGI ver 1.9 || OT2)

Symbols : WIDEn-N Digis are recommended to be updated to support NCAn-N and display a Green star symbol with an "S" overlay. Fillins Have a Green Star with a "1" overlay. The overlay and digi symbol are placed in the position beacon after the Lat & Long. The following position has a S# to indicate a S overlay Digi. (!DDMM.hhNSDDDMM.hhW#PHGphgdr/ W2, NCAn, We finally updated Intermod Ridge Digi to New Paradigm settings A=003900). Helpful links:Symbol Chart || Good PHGR calculator

TX Delay : 180 Milliseconds is recommended.

Trapping : Trap abusive paths from near or distant users. Settings will depend on individual geographic factors. Many digis are now trapping down to WIDE3-3, some high level digis even trap WIDE2-2. This gives abusive users one hop. A Northern California digi that constantly receives QRM from a WIDE5-3 beacon from out of State could trap it to one hop by using the UIDIGI command: KPC-3 (UIDIGI ON, WIDE2-2, WIDE3-3, WIDE3-2, WIDE5-3) Kantronics TNC's allow four trappable paths. || TNC-2 UIDIGI ver1.9 can have up to eight trappable paths: (UIDigiCall = WIDE5-4, WIDE5-3, WIDE4-4, WIDE4-3, WIDE4-2, WIDE3-3, WIDE3-2, WIDE2-2). || OpenTracker2's can trap hops of any WIDEn using HOPlimit, or set up to eight valid aliases with limits. || TinyTrack4's can allow up to three valid aliases:(WIDE1,WIDE2,NCA1) ignoring abusive paths.

Emergency Paths TEMP and SSn-N paths are usually not trapped, or restrained. New Paradigm digis in Northern California with a "S" overlay will Digipeat NCAn-N. An emergency message could be propagated throughout Northern California by using a Path of NCA3-3. A path of NCA3-3,SCA3-3 will blanket the whole State, not advisable for routine traffic. TEMP is encouraged to be enabled in fillin digis, Home stations, and mobiles. It can be enabled in Kenwood D700 radios. This gives us another backup network path. Routine use of TEMP is discouraged on 144.390 MHz, except on Field Day or during emergencies.